Alternators, particularly intended for vehicular use, and especially adapted to be installed in automotive vehicles, are subjected to weather and environmental influences which are potentially harmful to the interior thereof. The alternator has slip rings which, usually, are exposed to an air stream induced in the alternator to provide for cooling thereof. The resultant contamination of the slip rings, and hence of the contacting surfaces with current supply brushes for a field winding, cause difficulties in the operation of the alternator. It is particularly damaging to the alternator if humidity and moisture, especially if salt-laden, due to road salting, operation near the seacoast or the like, reach the interior of the alternator. The slip rings and the brushes should be protected from spray or other moisture penetration as much as possible.
Alternators, as currently constructed and especially for vehicular use, are usually assembled in a pot or cap-like construction, such that two end shields or end bells are secured together, holding a stator winding and core therebetween. The alternator shaft is retained in bearings in the end shields. One side of the shaft penetrates from the alternator towards the outside thereof, and at that end carries a V-belt pulley for coupling via a V-belt to an internal combustion engine. Usually, a fan blade or fan wheel is located adjacent the pulley to pull air essentially axially through the alternator to provide for cooling thereof. No special protection against contamination, dirt, and particularly against spray water, is provided.
It has previously been proposed to provide protection for the interior elements of the alternator against contamination--see U.S. Pat. No. 3,233,130--in which housing elements are shaped to extend, cup-like, into the interior thereof, and to, at least in part, cover the slip rings. Such a construction is expensive to make, complex to assemble and requires additional structural elements in order to provide a reasonable sealing space within the region in which the slip rings operate.
It has also been proposed--see British Pat. No. 1,149,856--to provide a cup-shaped sheet-metal housing. This, however, is not an alternator which is adapted particularly for vehicular use, that is, it is constructed of the customary pot-shaped construction. The alternator, as described in the British patent, has a housing part fitted on the cup-shaped sheet-metal housing which retains a plate with rectifiers and the brush holder. A cup-shaped extension is connected to this housing part which partially covers the slip rings.
Covering the space in which the slip rings operates has also been suggested by utilizing a structural component made of insulating material which, in combination with a disk-like thickening of the rotor shaft, forms a space which is protected against dust and spray water, to some extent at least--see U.S. Pat. No. 3,731,126. This space, simultaneously, also encloses the brush holder and the brushes themselves, and it is closed over the housing portion at the slip ring side of the generator housing. A seal against the interior of the alternator is provided by use of a felt seal, in ring form, which engages the insulating element. This seal is subject to wear, and has to be serviced from time to time. An additional holding ring is needed to retain the structure in place.